CD4+CD25+ regulatory T cells play a major role in the control of immunity, as the lack of this T cell population results in the activation of autoreactive T cells and the development of autoimmune diseases. It has been reported that the level of CD4+CD25+ regulatory T cells is lower in autoimmune-prone mice such as NZBxNZWFI (BWF1) and NOD mice. The central hypothesis of this proposal is that autoimmune-prone mice may have a defect in CD4+CD25+ regulatory T cell function which may play a role in the pathogenesis of autoimmune diseases. Our preliminary studies suggest that NOD antigen presenting cells (APC) play a crucial role in the defect of CD4+CD25+ regulatory T cell function, but that activation of NOD APC restores normal regulation in vivo. The objective of this proposal is, therefore, to develop novel strategies using TLRs to restore optimal regulation in NOD mice, and to characterize the mechanisms of this regulation. Moreover, we will investigate whether APC from diabetic patients have also a defect in activating regulatory T cells, and whether enhancement of their APC function can ameliorate regulation, as well as whether regulatory T cells from diabetic patients can be activated directly via TLRs.